Happy Epiphany!
We blessed chalk at church this morning to chalk our doors at home with the traditional greeting to the Wise Men, who have arrived at the crib today. It's a prayer for God's blessing on the house, and a sign that we are open to God's wisdom in all who come to our house.
The C, M and B are the initials of the tradional names for the wise men, who aren't named in the Bible - Caspar, Melchior and Balthasar . Alternatively they stand for
Christus Mansionem Benedicat - Christ bless this house.